[P3] No ESLint or Prettier configured

Problem

The project has no ESLint or Prettier configuration. This leads to inconsistent code style, missing linting checks for common bugs, and no automated formatting enforcement.

Files

• Project root — no .eslintrc*, .prettierrc*, or related config files

Acceptance Criteria

• Add ESLint configuration with recommended rules
• Add Prettier configuration
• Add lint and format scripts to package.json
• Configure VS Code settings for auto-format on save